1. Field of the Invention
This invention relates to refrigeration equipment and in particular, though not solely, to apparatus for controlling the cooling of refrigeration systems and control systems used therein.
2. Description of the Prior Art
Temperature control system used in some early refrigerators simply comprised a thermostat which ensured tat the compressor turned off when it required temperature was reached within the refrigerator. While this simple style of controller may have been sufficient in a single compartment refrigerator, it is not suitable in multiple compartment/multiple temperature zone cooling systems.
In a two compartment refrigerator/freezer, the temperatures of the two compartments are required to be maintained at selected but different temperatures. In order to accomplish this with a single evaporator, valves have been used to control the flow of cooling air to the various compartments from the evaporator so that each compartment receives sufficient cooling. An example of this type of system is disclosed in U.S. Pat. No. 4,481,787 assigned to Whirlpool Corporation. However, it is well known that this type of cooling system usually results in tie temperatures of the various compartments following each other or "tracking". An example of this behaviour is when a load of groceries are placed in the refrigerator or product compartment of a refrigerator/freezer. The compressor will be called upon to do more work on the refrigerant to lower the temperature of the evaporator so that cold air may be introduced to the product compartment to cool the new groceries. Accordingly, any air fed to the freezer compartment (either it is required because the temperature of the freezer compartment temporarily drops below its set temperature or due to "back pressure" from air flowing into the product compartment) will likely be at a temperature below the temperature required of the freezer compartment (which is already at its required temperature) and thus the freezer will be over cooled. The converse is also true when warm items are placed in the freezer compartment resulting in the product compartment being over cooled. In addition, prior multiple compartment cooling devices have not attempted to minimise energy consumption by ensuring that required compartment temperatures are reached at substantially the same time, allowing the compressor to only ever be used to cool both compartments at once and then to be turned off.
It is therefore an object of the present invention to provide a cooling device which will at least go some way towards overcoming the above disadvantages or which will at least provide the public with a useful choice.
Accordingly, in a first aspect, the invention consists in a cooling device comprising:
refrigeration plant means including condenser means, evaporator means and energisable compressor means,
compartments to be maintained at selected temperatures, a first of said compartments to be maintained at a first selected temperature and a second of said compartments to be maintained at a second selected temperature, each of said compartments having an inlet and an outlet,
an evaporator air flow passageway means which houses and is thereby cooled by said evaporator means,
air flow regulating means for each said one compartment, a first air flow regulating means provided to regulate air flow in said first compartment and a second air flow regulating means to regulate air flow in said second compartment, said air flow regulating means regulating the amount of cooling supplied to each of said compartments,
air flow supply passageways connecting the respective inlets of each of said compartments to said evaporator air flow passageway to allow air flow to said compartments,
air flow return passageways connecting the respective outlets of each of said compartments to said evaporator air flow passageway to allow air to flow from said compartments,
temperature sensing means in each of said compartments,
control means which receives input from each said temperature sensing means and outputs control signals to each said air flow regulating means to regulate the air flow generated by each said air flow regulating means in accordance with programmed instructions so that the temperature in each of said compartments reach their respective selected temperatures at substantially the same time.
In a second aspect, the invention consists in a method of operating a cooling device having
refrigeration plant means including condenser means, evaporator means and energisable compressor means,
two compartments to be maintained at selected temperatures, a first of said compartments to be maintained at a first selected temperature and a second of said compartments to be maintained at a second selected temperature, each of said compartments having an inlet and an outlet,
an evaporator air flow passageway means which houses and is thereby cooled by said evaporator means,
air flow regulating means for each said compartment, a first air flow regulating means provided to regulate air flow in said first compartment and a second air flow regulating means to regulate air flow in said second compartment, said air flow regulating means regulating the amount of cooling supplied to each of said air flow supply passageways connecting the respective inlets of each of said compartments to said evaporator air flow passageway to allow air to flow to said compartments,
air flow return passageways connecting the respective outlets of each of said compartments to said evaporator air flow passageway to allow air flow from said compartments,
temperature sensing means in each of said compartments, and
control means which receives input from each said temperature sensing means and outputs control signals to each said air flow regulating means to regulate the air flow generated by each said air flow regulating means in accordance with programmed instructions so that the temperature in each of said compartments reach their respective selected temperatures at substantially the same time, said programmed instructions comprising the steps of:
i) sensing the temperatures in each of said compartments,
ii) calculating, for each said compartment, a difference temperature value between the sensed temperature in that compartment and that compartment's selected temperature,
iii) determining the amount of regulation required by each said air flow regulating means in order that each of said compartments will substantially reach their selected temperatures at the same time,
iv) operating each said air flow regulating means at the determined amount of regulation,
v) repeating steps (i) to (v) until each compartment has reached its selected temperature, and
vi) de-energising said energisable compressor means and reducing the amount of regulation of each said air flow regulating means to zero.